The present invention relates to a composition that is useful to protect a metallic substrate, particularly aluminum.
The corrosion of metals used in airplanes induced by the action of acids, salts or atmospheric pollution is well known. Protective coatings for aluminum skinned aircraft begin with a surface pretreatment step which is intended to both clean the surface and prepare the surface for paint application. The coating system consists of a surface treatment, primer and topcoat. The corrosion protection function is performed mainly by the surface treatment and primer portions of the coating system. Such pretreatment steps may involve the application of many combinations of acid, alkaline, or solvent chemicals, all of which are acceptable practice according to ASTM D-1730. The current surface treatments of aluminum aerospace alloys are based on application of solutions containing hexavalent chromium compounds. In the application to aircraft, the entire aircraft is sprayed down with a chromium-based solution and there is a significant hazardous material waste associated with this process.
Consequently, it would be very advantageous to provide a chromium-free, environmentally benign, adhesion promoting composition for a metal substrate.
Accordingly, it is an object of the present invention to provide a novel surface treatment coating for metal pretreatment prior to the application of paint.
It is another object to provide a method for treating metal.
Other objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.